1. Field of the Invention
The invention relates to a supported ruthenium catalyst, a process for its preparation and a process for the preparation of optionally substituted cyclohexylamine and optionally substituted dicyclohexylamine by the catalytic hydrogenation of optionally substituted aniline using a catalyst of this type.
2. Description of the Related Art
It is known to prepare cyclohexylamine by pressure hydrogenation of aniline. Cobalt catalysts containing a basic additive (British Pat. No. 969,542) and also Raney cobalt (Japanese Patent 68/03180) are employed for this hydrogenation. A ruthenium catalyst moderated with alkali and supported on an inert material is used, in accordance with U.S. Pat. No. 3,636,108, for the ring-hydrogenation of aromatic amino compounds, NH.sub.3 and, if appropriate, a solvent being employed in addition. Another process for the pressure hydrogenation of aniline to cyclohexylamine is described in DE-AS (German Published Specification) 1,106,319, in which a ruthenium catalyst is also used. Dicyclohexylamine formed at the same time is recycled to the feed material in this process; the process causes considerable losses through the simultaneous formation of cyclohexane. Finally, EP 53,818 considers that supported palladium catalysts are more advantageous than ruthenium catalysts for the pressure hydrogenation of aniline.
In the known pressure hydrogenation processes of aniline, dicyclohexylamine is only formed as a by-product together with cyclohexylamine. In order to obtain dicyclohexylamine in larger amounts, it is prepared by separate processes. Thus it can be obtained, for example, by the pressure hydrogenation of diphenylamine using a ruthenium/Al.sub.2 O.sub.3 catalyst (DE-AS (German Published Specification) 1,106,319). Dicyclohexylamine is also formed in the reaction of cyclohexanone with cyclohexylamine in the presence of palladium-on-charcoal under a hydrogen pressure of 4 bar (French Patent 1,333,692). Dicyclohexylamine can be obtained in a complicated process from the hydrogenation product of aniline over a nickel catalyst by fractional condensing out. Part of the ammonia formed at the same time is removed from the residual mixture, and the remainder is recycled to the reaction (German Patent Specification 805,518).
A common problem in all processes for the ring-hydrogenation of aromatic amines consists in the formation, which in some cases is considerable, of cyclohexane as a waste product which cannot be used further.
It was therefore desired to develop a new process, capable also of being used on an industrial scale, in which both cyclohexylamine and dicyclohexylamine can be produced in a desired ratio in one reaction stage, in which the loss caused by the formation of cyclohexane is repressed and in which, furthermore, the service life of the catalyst used is improved.